Inkjet printers operate by expelling droplets of ink onto the media from the printhead, which is the part of the printer that actually prints on a medium, and which generally has a two dimensional array of very small nozzles substantially parallel to the media. The printhead generally does not extend across the width of the printer; instead the printhead is generally mounted on a carriage, which slides sideways across the printer on a carriage rod and an anti-rotation rail (which prevents rotation of the carriage about the carriage rod) that extend across the width of the printer. Therefore, the printhead can print to the width of the media. The media is generally advanced perpendicularly to the dimension in which the printhead carrying carriage slides (i.e. advanced along the length of the media) so that substantially the whole of the media can be printed to.
When the printhead is printing to the media, the further the droplets expelled from the printhead must travel, the lower the resolution achieved in the resulting printout due to lateral movement of the droplets between the printhead and the media. However, if the printhead is brought too close to the media, any warping of the media when the droplets land and temporarily dampen the media could cause the media to come into contact with the printhead, which can lead to smudging of the printed media or even clogging of the printhead.
In order to optimise the so-called printhead-to-media spacing, the printhead must be sufficiently close to the medium that it will print to that medium without loss of resolution, and sufficiently far away from the media to avoid the media warping and touching the printhead. Therefore, there is generally an optimal printhead-to-media spacing for a printhead.
In a conventional inkjet printer, the printhead-to-media spacing is generally set so that the printing is optimised for plain paper as the medium to be printed on, as this is the most often used medium. However, if an envelope, or cardboard, is to be printed on, the extra thickness of the medium will make the printhead-to-media spacing too small, leading to problems outlined above. Additionally, if the printhead-to-media spacing is optimised for envelopes, cardboard or other such thick media then, when printing on thin media such as paper, the printhead-to-media spacing will be too large, leading to other associated problems mentioned above.